docs: def mxm(m1, m2):
      """
      Multiply two 3x3 matrices.
  
      http://naif.jpl.nasa.gov/pub/naif/toolkit_docs/C/cspice/mxm_c.html
  
      :param m1: 3x3 double precision matrix.
      :type m1: 3x3-Element Array of floats
      :param m2: 3x3 double precision matrix.
      :type m2: 3x3-Element Array of floats
      :return: 3x3 double precision matrix.
      :rtype: 3x3-Element Array of floats
      """
      m1 = stypes.toDoubleMatrix(m1)
      m2 = stypes.toDoubleMatrix(m2)
      mout = stypes.emptyDoubleMatrix()
      libspice.mxm_c(m1, m2, mout)
      return stypes.cMatrixToNumpy(mout)